Capacity control for air conditioning systems



0a. 21, 1952 MQ R TH 2,614,394

CAPACITY CONTROL FOR AIR CONDITIONINGVSYSTEMS Filed Nov. 20, 1946 -2 Sl-lEETS-Sl-IEET 1 Oct. 21, 1952 W. L. McgR Ti-l CAPACITY; CONTROL FOR AIR CONDITIONING SYSTEMS 2 'SI-iE 'r's-SHE T 2 Filed Nov. 20, 1946 FIG.4

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Y B l/ m 4 Ffl w 2 3 l0 5 4 Patented Oct. 21, 1952 CAPACITY CONTROL FOR AIR CONDI- TIONING SYSTEMS William'L. ltlcGrath, Syracuse, N. Y., assignor to Carrier Corporation, Syracuse,; N. Y., a corpo- 1 ration of Delaware- 7 Claims.

This invention relates to a system o'f-capacity control and, more particularly, to an air conditioning system in which means-are provided for attaining capacity control. v

Accurate capacity control of air conditioning systems is necessary to obviate unsatisfactory performanceunder conditions ofpartial'load. 'Unsatisfactory performance under conditions of 1 partial load is a handicap inherent in many comfort cooling systems, and is-a factor making for public dissatisfaction. In cooling air, the maintenance of asteady state condition requires matching the capacity of the equipment'which performsthe cooling'against the loadj' in other words, heat must be removed by the cooling equipment at the same average rate at which it missiblelimits of variation. In the cooling of air,"

it'isess'entialto effect necessary removal of undesirable absolute humidity while providing for delivery of the :dehumidified air at a dry 'bulb temperature not too cold for comfort.

Various attempts have been made" to solve the problem." For example, regulation of the compressor: has been attempted to reducethe useful pumping effect of the refrigerating machine in accordance-with changes 'inevaporator load.

Frequently, such procedure is unsatisfactory, for merely changing the useful pumping effect necessarily changes the temperature of the evaporator surface and, consequently, the moisture condition of the air passing therethrough, even thougha" desired dry bulb temperature can be obtained.

Regulation of theevaporator has also "been attempted. Such regulation is often undesirable for freezing results if the system be operated at a sufiiciently low5temperature to remove all the necessary 'moisture.- -If the air passing through the evaporator is cooled only partially, not below its dew point, as, forexample, under partial load some moisture removal, then insufficient moisture will be removed. to obtain the ."desired' relative humidity, and clammy ordamp conditions will result. Similarly, the use *of; systems "employing large .physical bypassesis not viewed' favorably because of the large equipment and 'centralsta tion systems required, wasting or rendering unavailable useful space.

I ApplicationNovember 20, 1946, Serial No. 711,156

(o1.-ez a) Another method heretofore employed require the" use of steam for reheat purposes; that is, the

refrigerating machine may operate at capacity to provide automatically the desired; dew-point o for moisture control regardless of variations in load, but the air subsequentto dehumidificationat a relatively low temperature is reheated with steam to provide a comfortable final temperature.

While this proposal provides adequate conditions,

the additional coils and equipment required are excessively large and expensive to install and operate since all of the air is first dehumidified and then all of the air is reheated. and circulated. Steam is not always readily available during summer and intermediate season conditions in many business establishmentsand in residences; in addition, the costof the steam employed for reheat purposes serves to increase considerably the total cost of conditioning air supplied to the structure being treated.

A principal object of this'invention is to eliminate disadvantages inherent inprevious methods and to provide means for obtainingcapacity controlof air conditioning systems;

An object of the invention is to provide -arefrigeration system including meansfor varying thecapacity of the system in response to the load imposed thereon, while permitting desired final conditions of temperature and humidity to be obtained underconditions-of partial load.

A further object is to provide an air conditioning system in which the rate of moisture removal as well as the rate of sensible heat absorption may be correlated I and desirably controlled.

"A stillfurther object'is to provide a refrigeration-system including reheat control without m I creasing the coil-surface required in the system.

A still .furthe'r'object is :to provide a refrigeration system embodying self-compensating control means' for varying-the capacity thereof in accordance with the load imposed on the system. Other objects of my inventionwill be readily perceived from the following description. i 1

This invention relates to a refrigeration system which comprises, in combination, a compressor,

a condenser, and an evaporator disposed in -a closed circuit, means in said circuit for metering the amount oficondensed or cooling refrigerant passing to the evaporator, the evaporator including" a plu'rality of separate passages for the evap--' oration ;of refrigerant, means connecting the compressor with on'ei-of said passages, and control means for regulating the fiowlofheating fluid from the compressor-to another of i said evaporatorpassages. If desired, automatic means may of said passages, and control mean for regulating the supply of heating fluid from the compressor to such passage.

This invention further relates to a method of providing capacity control for an air conditioning system in which the steps comprisepassing cool-,=

ing or condensed fluid to a plurality of passages in an evaporator to adjust the temperature and moisture content of air passing through the evaporator;"discontinuing, in response to a decrease in .the temperature "of. air passing therethrough',the"supply of cooling or condensed'fluid to at-leasta portion of one of said passages While continuing-todirectv cooling "fluid into the remainingpassa'ges; and passing heating fluid into at'lea'st a portion of said passages in response to a further decrease in the temperature of air directed therethrough.

The-attached drawings illustrate certain "preferred emb'odimentsof. my invention, in which Figure'il is'a diagrammatic view of the rte-- frigerating--.:and-:air conditioning system of my invention; T

Figure 2 is a diagrammatic view of a refrigerating andair'conditioning system, similar to Figure Lillustratihg a modified form of evaporator;

Figure 3 is a diagrammatic view of a refrigeratingx-iiand air conditioning system, similar to Figure 1, illustrating a modified form ofcontro'lmeans:

Figiire'iis a sectionalview of a controlvalve for-use in the system; .and-

Figure 5 is a diagrammatic view of a modification-of the invention;

Referring :to the drawings, there is illustrated in Figure 1 a refrigerating "system which comprisesua compressor 2 connected to a condenser 3 byzdiseharge line4. A-liquid receiver 5 maybe providedto receive condensed refrigerant' from condenser 3. Liquid line 6 connects receiver 5 to an;evaporator"|. Disposedin-line 6 isa thermal expansion valve 8 of usual construction adapted Any suitable types of restrictions" pressor -2. Thermal-bulb '14 is disposed adj acent suction line l3 and is responsive to superheat-of refrigerant leaving evaporator T to control the operation of expansion-valve't in the usual-man-' ner. 1 v

Evaporator 1 contains-a plurality of separate sections 15 and; forming passages for refrigerant.- Section l5-of evaporator! is; connected to line 6 by line 9,--and isconnected-to' suction line;

I3. I Expansion valve 8 and restriction l l'regulatez 1 the amount'of refrigerant passing intosection l5.

The-gaseousrefrigerantirbm section l'5 passes into line 13 and is drawn into compressor-2.

Section 6 includes portion lta'which extends across the leaving air end of evaporator 1, portion I60 which extends through the evaporator and portion l to which passes across the evaporator at the entering air end of the evaporator. Portion 6b of section it is connected to line 6 by means of line in. Portion 16b of section 16 is connected to suction line [3 leading to compressor 2.

Control means I! is connected to section I6 .for a purpose hereinafter described. Preferably,

control I! is connected to section I6 between the leaving air side of evaporator I and the entering air side of the evaporator. The direction of air passing-through the evaporator is shown by the arrow? The control-means I! may be actuated automatically by'means of a temperature responsive element .T disposed, for example, in the path of air entering evaporator l. A line l8 connects compressor 2 with control means 11, and portion 16a of section I6, depending upon the operation of control means 11.

It will bev understood control means I! may comprise pneumatic valves or solenoid valves, for

example, but preferably control means 17' consists of an automatically operable three-Way valve, shown in Figure 4. The valve shown ,in-

Figure t comprises a casing 19 containinganinlet passage 20 adapted to receive refrigerant from line I0 and the leaving air portion Ifia of section 16, such refrigerant passing through the valve and outlet 2| to the entering air portion IBb of section Hi; the refrigerant then passes into suction line I3 and is'returned to compressor 2.

A second inlet 22 is provided which permits the entrance oi-hot refrigerant gas from compressor- 2 into the valve.

A plate 23 separates the upper and lower por-' tions of the valve.v A bellows 24 is disposed in the upper portion of the valve and is connected to a second plate 25. Spring 26 is disposed in mined pressure upon bellows/'24.

connects ,theinterior of bellows '24 with tube 29 connecting it to bulb T. Expansion" and contraction ofbellows 24 is controlled-by means of vapor pressure of fluidin-bulb T. Spring .26 is disposed insuch a manner asto oppose-the expansion'of-bellows 24. It will be-understood suit.- able manual controls may. be-provided in place i of bulb T.

A red Blisattachedat one end to plate-25- Rods 32 and 33 are provided onoppositeends of whiflietree-3lv vOne end ofrod 32 is disposed in guide; 34 attached to plate-23-, and one end of rod 33" is disposed in guide 35, alsoattached to plate 23. A valve member 3B'is secured to the opposite end 1 of rod-32-and is adapted to co-operate with valve seat-.31; to=preven t passage 'of fluid between'inlet' and, at its opposite end-to a whiftletree -3 I ZDand outlet 2|; Rod 33 carries valve member 38- ;at its opposite'end. Valve member 38 is adaptedto co-operate with valve seat-39 to prevent refri'gerr ant, entering the housing through inlet 22," from passingthrough thewvalve.

Ii-desired, as'shown iii-Figure 5,-a bypass line to andsuitable control means 4| may be provided to'varythe temperature of evaporator] by feed- .75 to the evaporator.

*Under full load conditions, the operation of the'system is as follows: Hot compressed gaseous refrigerant from compressor 2 passes through'line 4 to condenser 3, is condensed and passes to receiver 5. Liquid refrigerant passes from receiver 5 through liquid line 6 to expansion valve 8;- from expansion valve 8 refrigerant flows through lines 9 and lit to the various evaporator sections l5 and I6. Restrictions II and I2 disposed in lines 9 and [0, respectively, serve to establish a decrease in pressure of refrigerant passing to the evaporator sections I5 and I6. Air passes through the evaporator I in the direction' of the arrow. The expanded refrigerant flows intothe sections l5 and I6, and-cools or decreases the temperature of air passing through the evaporator below its dew-point, thereby'decreasing the amount of moisture carried by such air. The gaseous refrigerant formed in the evaporator sections then passes by suction line 13 to compressor 2. 1

Assume there is a drop in temperature of air being directed through evaporator 1. I Thermal element T, as shown, is responsive to the temperature of air being directed to evaporator 1, although it will be understood it may be respongive to temperature of return air or the like or, if desired, element T may be placed in a room being conditioned to respond to temperature of the air in the room; element T controls the operation of valve ll. Upon a decrease in temperature of such air, element T actuates valve ll toclose section I6 to the passage of condensed refrigerant (refrigerant from line l). Assuming the temperature of air directed to the evap'orator continues to decrease, element T actuates valve I! to open inlet 22 permitting hot gaseous refrigerant from compressor 2 to pass to section IE to heat the air passing therethrough. The hot gaseous refrigerant supplied to coil 16 causes pressure to increase in such coil. When the pressure in the coil increases to a point equal to the saturation pressure corresponding to the dry bulb temperature of the air leaving the remaining section or sections of the evaporator, as shownin Figure l, condensation of the gaseous refrigerant begins. The condensed refrigerant flows through restriction l2 into line 9 and into evaporator section l where it is re-evaporated and used to cool and to dehumidify air passing through such portion of the evaporator. Under some conditions, insufficient liquid is condensed in section 16 to supply the requirements of section l5. In such a'case, expansion valve 8 opens sufficiently to supply any required amount of liquid refrigerant to section [5.

If the temperature of the air passingthrough the'evaporator continues to decrease, more hot gaseous refrigerant from compressor 2is supplied to section 16 thus causing pressure in section I6 to'increase. As the pressure in section I 6 increases, gaseous fluid therein condenses at a higher temperature and thus raises the dry bulb temperature of the air leaving such portion of the evaporator. As the temperatureof air directed to the evaporator increases, valve I1 serves to decrease the amount of gaeous refrigerant passing into section l6. Upon a further increase in temperature of such air, valve l1 closes gradually and prevents passage of hotgas into section I6 and will then gradually open outlet 2| and permit condensed refrigerant to pass through section l6 to suction line l3 until capacity-balance is again established.

In Figure 2, I have shown another embodiment of the invention including a modified form of heat exchange surface. --In the'system shown in Figure 2, evaporator I comprises a plurality of sections 42, 43, and44. As illustrated, section 42isdisposed at the leaving air end of the evaporator]. Refrigerant passes through restriction H and line 9 into sections 43 and 44, the evaporated refrigerant passing into suction linel3 and returning .to compressor 2. Condensed refrigerant passes through restriction l2 into line l0 and through coil 42 to suction line [3 to be returned to compressor 2.- The above description'contemplates normal operation of the evaporator. at full load.

Line l8 connects compressor 2witn coil 42 of evaporator .1. Heating fiuid passes through line l8 and control valve IT into section 42. Bulb T is responsive to the temperature of air directed to the evaporator; in response to decrease in such temperature, it actuates valve [1 to shut off coil- 42 from suction line l3. A further decrease in temperature of air directed to evaporator 1 causes control valve I! to open gradually, permitting hot gas from compressor 2 to be supplied to coil 42. Restriction I2 in line In prevents such gas from flowing back through the coil in any substantial quantity. Pressure in section 42 begins to increase; Whe lts rises to a point equal to the saturation pressure corresponding to the dry bulb temperature of air leaving sections 43 and 44, condensation in section 42 begins. -As a result of such condensation, the temperature of air leaving evaporator l is increased; liquid refrigerant condensed'in coil 42 flows through restriction l2 into sections 43 and 44, where it will be again evaporatedand used to cool and to dehumidify airpassing through such coils. As air temperature continues to decrease, the valve port in control means I! opens still wider and permits pressure in coil-42 to increase, thereby condensing refrigerant at a higher temperature and further increasing the dry bulb temperature of air leaving theevaporator.

In the heat exchanger or evaporator illustrated in Figure 2, there exists a theoretical possibility that wet gas may be discharged into suction line l3, reducing the superheat in the suction line causing the thermal expansion valve to throttle the flow of refrigerant. This may result in a lower evaporator pressure during the period valve I1 is exerting a throttling action. This is not a serious disadvantage so long as the proportion of heat exchange surface used is small; the reduction in suction pressure will not be so great as to cause frosting on the coil. If the valve closes rapidly as by snap-action, this disadvantage is eliminated. The effect is eliminated completely by the heat exchange structure shown in Figure 1 in which a clean-up section is provided on the entering air side of the evaporator. In such structure, as the valve I'I throttles, any liquid refrigerant which passes into this portion of section [6 is immediately evaporated; thus, the operation of the expansion valve B-is not affected by wet gas entering the suction line during the time valve l1 exerts a throttling action.

It will be appreciated an automatic control valve as illustrated in Figure 4 is not essential in my invention. In Figure 3, I have illustrated a system utilizing pneumatic control valves 46 and 46 in place of control valve II. In other respects, the system illustrated is similar to the system shown in Figure 1. In operation, valve 45 is closed gradually, and then valve 46 is opened graduallyupon a drop; in temperature of the, air passingthrough thev evaporator, room temperature, or the. like. Upon a rise in temperature, valve lfi is closed gradually, and then valve 45 is opened.

My; invention provides a simple, ready, and inexpensive means ofattaining capacity control air conditioning systems; if desired, such means may be readily included in the equipment at the place of manufacture or at the place of use. Extensive or expensive additional equipment is not required since the invention utilizedaportion of the existing heat exchange surface. Such portion, of course, at partial load is not required for cooling purposes. Utilization of a portion of the evaporator coil eliminates the additional space requiredand an increase in air resistance obtained if additional heat exchange surface were provided. The invention obviates clammy, mu gy, or damp conditions under partial load and provides capacity control by the use of reheated or dehumidified air without requiring the use of additional coils or coil surface for heat exchange purposes. The rate of moisture removal, as well as the rate of sensible heat absorption. is controlled even under conditions of partial load of the equipment. The capacity of the system' maybe varied in response to the load imposed thereon, thus obviating unsatisfactory performance under conditions of partial load.

WhileI have described and illustrated certain preferred embodiments of my invention, it will be understood my invention is not limited thereto since it may be otherwise embodied Within the scope of the following claims.

I claim:

1. In a system of the character described, the

combination of a compressor, a condenser con nected to said compressor, a heat exchanger connected to said condenser, a suction line connecting-said exchanger with said compressor, said exchanger including a plurality of sections for the evaporation of cooling fluid, expansion means for regulating the amount of cooling fluid passing to the. exchanger, a plurality of lines connecting said means with said evaporator'sections, con strictions in said lines connecting the regulating means with the evaporator sections restricting the amount of cooling fluid passing into said sections, a heating fluid line connecting the compressor with one of said exchanger sections, control means for controlling the passage of heating fluid from the compressor to said exchanger sec tion, a temperature responsive bulb for actuating saidcontrol means, said control means, in response to a decrease in temperature indicated by said bulb. decreasing, the amount of cooling fluid passingjinto. said section, and, in response to a further decrease in such temperature indicated by-said bulb, discontinuing the'passage of cooling fluid therethrough and permitting the passage of heating fluid onlytherein, said control means at substantially full capacity operation preventing the passage of heating fluid from the compressor to said exchanger section while permitting the passage of cooling fluid only.

2. In a system of the character described, the combination of acompressor, a condenser, a discharge line connecting said compressor and said condenser, a heat exchanger having a plurality of sections for the passage of fluid therethr-ough, a suction line connecting said compressor with said exchanger, an expansion valve disposed in a line connecting the condenser and the exchanger, a plurality of lines connecting said expansion valve withjsaid exchanger sections, constrictions in said connecting lines disposed between the exchanger sections and said expansion valve for distributing the cooling fluid passing to-saidsections, a temperature responsive element for controlling the operation of saidexpansion valve, said element being disposed adjacent said. suction' line,.one of said exchanger sections extending through the-leaving air end of said exchanger-and then through the entering air end, said exchanger being connected to the suction line, a control valveadapted to open: and close said exchanger section which-extends through the entering air end of the exchanger and through the leavingair end automatically to the passage of cooling'fluid, a line directly connecting. said compressor with said control valve, and a second temperature responsive element disposed inthe path of air being directed to the exchanger for controlling the operation of said control valve, said control valve serving automatically to close said section to the passage of cooling fluidasthe'temperature of air-being directed to the exchanger tends to decrease and, as the temperatureof air being directed to saidexcha-nger tends to further decrease, connecting at least a portion of said section with the compressor to-permit the passage of heating fluid into the leaving air end portion of said section thereby reheat ing air passing'through the exchanger.

3. In a refrigerationsystem, the combination of a compressor, a condenser, a heat exchanger, and means for metering the amount of cooling fluid passing to said exchanger, said compressor, condenser, exchanger and metering means forming a closed circuit, said-exchanger including a plurality of separate sections, one of said exchanger sections extendingthrough the leaving air portion of said exchanger and then through the entering air portion of said exchanger, the entering air portion of said section being connected to a suction line leading tothe compressor under normal conditions of operation refrigerant flowing through .the leaving air. portion andthen through the entering air. portion to thesuction line,.a second line connecting said section having a leaving air portion directly to said compressor to permit heating. fluid vtopass .from the compressor into the leaving air portion of said section, and means for controlling-the. passageof heating fluidfrom the compressor into the leaving air portion of said section, heating fluid condensing in theleav'ing air portion and passi'ngtothe remaining sections of the exchanger.

4. In a method of providing capacity control for adirect expansion air conditioningsystem, the steps. which comprise passing condensed fluid through a plurality of separate sections in an evaporator to adjust the=temperature and mcistureicontent of air passing therethrough; reducing the amount of condensed fluidpassing through one of said sections in response to a decrease inithe. temperature of air directed to the evaporator; then discontinuing the passage ofcondensed fluid to said section receiving a reduced amountof condensed fluid; permitting the assageof heating fluid in, said section to which passage of condensed fluid has been discontinued in response to a further decrease in the temperature of air directed,to the evaporator; permitting the pressure of heating fluid in said section to increase untilvpassage :of air therethrough liquefies the fluid to some extent while reducing the moisture content of such air; and permitting the passage of the liquid to the remaining sections of the evaporator to cool air passing therethrough;

5. In a method of providing capacity control for a direct expansion air conditioning system, the steps which consist in passing liquid refrigerant into a plurality of separate sections in an evaporator to adjust the temperature and moisture content of air passing through the evaporator; reducing the amount of liquid refrigerant passing into one of the sections in response to a decrease in the temperature of air directed to the evaporator; then discontinuing passage of liquid refrigerant to said section receiving a reduced amount ofv liquid refrigerant in response to a further decrease in the temper-ature of air directed to the evaporator; and

passing hot gaseous refrigerant into said section in which passage of liquid refrigerant has been discontinued to heat the air passing therethrough.

-6. In a method of providing capacity control for a direct expansion air conditioning system, the steps which consist in passing liquid refrigerant into a plurality of separate sections in an evaporator to adjust the temperature and moisture content of air passing through the evaporator, one section of said evaporator having a portion extending through the entering air end of the evaporator and a second portion extending through the leaving air end of the evaporator; reducing the amount of liquid refrigerant passing into the leaving air portion of said section in response to a decrease in the temperature of air directed to the evaporator; then discontinuing passage of liquid refrigerant to the leaving air end of said section in response to a further decrease in the temperature of air directed to the evaporator; passing hot gaseous refrigerant into the leaving air portion of said section, permitting the pressure of the hot gaseous refrigerant in said leaving air portion to increase until passage of air therethrough liquefies the gaseous refrigerant to some extent, and passing the liquid refrigerant from the leaving air portion of said section to remaining sections of the evaporator.

7. In a refrigeration system, the combination of a compress-or, a condenser connected to said compressor, a heat exchanger connected to the condenser for adjusting the temperature and moisture content of air passing therethrough, said exchanger including a plurality of sections, one of said sections having a portion extendin through the leaving air end of the evaporator and a second portion extending through the entering air end of the evaporator. a suction line connecting the sections of the evaporator with the compressor, means for metering the amount of cooling fluid passing to the evaporator, a heating fluid line connecting the compressor with the section portion placed in the leaving air end of the evaporator, and control means for controlling the passage of heating fluid from the compressor to said section portion placed in the leaving air end of the evaporator.

WILLIAM L. McGRATH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,195,781 Newton Apr. 2, 1940 2,344,215 Soling et al Mar. 14, 1944 2,403,818 McGrath July 9, 1946 2,451,385 Groat Oct. 12, 1948 2,515,842 Swinburne July 18, 1950 

